This proposal describes the framework of an R01 grant by Dr. Daniel Lingwood, an Assistant Professor at Harvard Medical School and faculty member of the Ragon Institute of MGH, MIT and Harvard, and Dr. Bryce Chackerian, an Associate Professor in the Department of Molecular Genetics & Microbiology at the University of New Mexico School of Medicine. Their research centers on B cell antigen recognition (Lingwood) and directed evolution of virus-like particle (VLP) vaccine platforms (Chackerian). Together they propose to develop a key vaccine-priming step that will predispose for elicitation of broadly neutralizing antibody (bnAb) responses to HIV-1. Recent data has shown that when humanized mice are genetically constrained to use the antibody VH gene IGHV1-202, early stages of VRC01-class responses are observed following immunization with the HIV-1 envelope glycoprotein (Env). VRC01-class antibodies neutralize ~90% of viral stains through a remarkable converge of structure aimed at CD4 receptor mimicry and engagement of Env. This group of antibodies is found in multiple infected individuals and always arises via use of IGVH1-202, suggesting there may be a mechanistic basis for specific bnAb development. The humanized mouse data indicates that vaccine- induced VRC01-like responses may be possible in humans if the responding antibody repertoire can be initially biased towards IGHV1-202, akin to the genetically engineered VH-restriction in mice. However, selective targeting and expansion of a VH-specific B cell pool is challenging as the germline B cell receptor (BCR) consists of hypervariable features, most notably, the stochastically-derived CDRH3 loop which dominates antigen-interactions. In this application, Dr. Lingwood and Dr. Chackerian propose to engineer IGVH1-202- selective B cell priming agents by evolving VLPs that display multivalent and high affinity binding to a specific genetically encoded feature of this B cell lineage, its CDRH2 loop. This motif forms the critical contact engendering broad neutralization of HIV-1 during VRC01-class development. The research team has already shown that their RNA bacteriophage technology for peptide display and affinity selection can be applied to generate VLPs which target and activate specific BCR sequences in vitro, and that these VLPs are immunogenic in transgenic mice expressing the complete human antibody repertoire. Dr. Lingwood and Dr. Chackerian will now apply this pipeline to develop and test whether VLP immunogens, by virtue of engineered high affinity for a genetically preserved BCR motif, can selectively prime the IGVH1-202 B cell response. If successful, the team will have developed both generalized methodology for expanding VH-specific B cells of interest and in the case of IGHV1-202, will have provided the first step and critical component of a vaccine to initiate VRC01-class responses in humans. Exploiting genetic bases for bnAb elicitation aims to overcome the failure of traditional approaches to HIV-1 vaccination and is consistent with the purpose of this funding opportunity and broader mission of the NIH.